Dendritic cells (DCs) are specialized antigen-presenting cells with the ability to internalize antigen, and present antigen-derived peptides to T cells. The functions of DCs depend on the subset, as well as their location and activation state. Immature DCs act as sentinels by continuously sampling the antigenic environment through various endocytosing mechanisms. The aim of this thesis was to investigate the use of dealuminated zeolites as a delivery tool to study the early events during endocytosis, including recognition and uptake, in human DCs. In the first study, we showed that dealuminated zeoilte particles can be used to follow endosomal acidification and proteolysis in human peripheral blood DCs. In the following studies we further investigated zeolite particles, and showed that they have a unique capacity to adsorb various biomolecules, proteins as well as differently charged lipids. This feature makes zeolites an ideal tool to study receptor-mediated endocytosis. Using zeolites coated with different ligands, we could show major differences in the endocytic capacity in human blood plasmacytoid DCs (pDCs) and myeloid DCs (mDCs). The pDCs showed an almost complete lack of endocytosis whereas the mDCs had an efficient selective receptor-mediated endocytosis of IgG-, LTA-, and LPS-coated zeolite particles. Furthermore, capture was strongly dependent upon the density of the ligands adsorbed onto the zeolite particles. In the last study, we used zeolites to compare endocytosing capacity in mDC and MoDC (monocyte-derived DC). We could show that these cell populations differ considerably in their ability to capture particles, immune complexes and soluble molecules. Therefore, in vitro generated MoDCs does not seem to be an applicable model for peripheral blood mDCs when studying the early events of endocytosis. In conclusion, zeolite particles provide a valuable tool to gain more understanding of the endocytosing mechanisms not only in DCs but also in other endocytosing cell populations.

The mononuclear phagocyte cell system includes monocytes, macrophages anddendritic cells which are important cells in order to recognize, ingest, destroyand also present part of a pathogen to T-lymphocytes in order to activate theadaptive immune system. Dendritic cells (DCs) stand out in their ability tostimulate T-lymphocytes and are also believed to be important to keeptolerance for “self-antigens”.Therefore DCs are of interest for use in immunotherapy studies. However inmost such studies to date, DC-like cells have been used, so called monocytederived dendritic cells (moDCs).The aim of this thesis was to investigate the early events following in vitroactivation of highly purified human DCs. In the first study we observed thatthe production of IL-8 and down regulation of CD128b preceded surfaceexpression of MHC class II and CD40, 80 and 86. We have in the followingstudies used and demonstrated the practical use of zeolite particles as ligandcarriers with the purpose to study the uptake mechanisms deployed byphagocytes. We show the advantage of using zeolite particles, due to theirability to bind various types of ligands i.e. proteins, oligonucleotides,lipophilic, and hydrophobic molecules. In addition, we have adsorbed biomolecules in sequential steps, which demonstrates the potential of coadsorbing ligands e.g. for targeting a specific endosomal compartmenttogether with molecules sensing the endosomal microenvironment.Coating zeolite particles with different biomolecules might provide furtherunderstanding of mechanisms involved in antigen sorting into endocyticcompartments.